Source of power supply of plasmatron arc

ABSTRACT

An inductive-capacitance current stabilizer has an input which is connected with the primary windings of a transformer which has two groups of secondary windings. The windings of one group are power windings and are connected through a rectifier to the arc gap of a cathode-article of a plasmatron. The windings of the other group are auxiliary windings, magnetically coupled with the transformer power windings through a transformer core and connected to a capacitor through an auxiliary rectifier.

United States Patent 1191 Volkov et a1.

SOURCE OF POWER SUPPLY OF PLASMATRON ARC Inventors: Igor Vladimirovich Volkov, ulitsa Filed:

Saxaganskogo, 90, kv. 112; Eduard Migranovich Esibian, ulitsa Kapitanovskaya, 6, kv. 47; Mikhail Mikhailovich Alexandrov, ulitsa Bratskaya, 10, kv. 28; Stanislav Ivanovich Zakrevsky, ulitsa Vemadskogo, 61, kv. 92; Petr Grigorievich Zhukovsky, ulitsa Parkhomenko, 60, kv. 49, all of Kiev, U.S.S.R.

Apr. 18, 1974 Appl. No.: 462,091

Related US. Application Data Continuation of Ser. No. 305.185, Nov. 9, 1972,

abandoned.

U.S.Cl. ..323/6; 219/121 P,3l5/111.2, 323/60; 323/88; 323/50 Int. Cl G051 1/02; H01j 7/24 Field of Search 323/6, 50, 60, 61, 88,

WR, 131 R, 135', 315/1112 lNDUCTANCE-CAPACITANCE CURRENT STABILIZER [45] Nov. 4, 1975 [56] References Cited UNITED STATES PATENTS 3.125,?03 3/1964 Rebuffoni et a1 H 219/131 WR 3,284,696 11/1966 Nagata et al 323/50 3,316,381 4/1967 Gibson 219/131 R 3,577,030 5/1971 CuSiCk et a1. 315/1112 3,781,508 12/1973 Dauer et a1 219/121 P 3,809.850 5/1974 Saenger, Jr 219/121 P FOREIGN PATENTS OR APPLlCATlONS 43-425 1/1968 Japan 219/135 Primary Examiner-Gera1d Goldberg Attorney, Agent, or FirmWaters, Schwartz & Nissen [57} ABSTRACT An inductive-capacitance current stabilizer has an input which is connected with the primary windings of a transformer which has two groups of secondary windings. The windings of one group are power windings and are connected through a rectifier to the arc gap of a cathode-article of a plasmatron. The windings of the other group are auxiliary windings, magnetically coupled with the transformer power windings through a transformer core and connected to a capacitor through an auxiliary rectifier.

4 Claims, 2 Drawing Figures U.S. Patent Nov. 4, 1975 3,917,992

lNDUCTANCE-CAPACITANCE [0 CURRENT STABILIZER SOURCE OF POWER SUPPLY OF PLASMATRON ARC This is a continuation of application Ser. No. 305,185, filed Nov. 9, [972 and now abandoned.

The present invention relates to an improvement in power supply sources for plasmatron arcs with stabilized currents.

Commonly known is a plasmatron are power supply source utilizing an inductive-capacitance current stabilizer for stabilizing arc current. The stabilizer inputs are connected across the power supply, while its outputs are connected through a transformer across a rectifier connected to the plasmatron electrodes which constitute the plasmatron cathode and the article being processed. With such a power supply source, the arc current is controlled in steps, by switching over the turns of the transformer windings. For details reference can be made to Inductive-Capacitance Converters" A. N. Nilekh, B. E. Kubyshkin, l. V. Volkov, Naukova Dumka Publishers, Kiev 1964).

For supplying plasmatrons of higher ratings (currents exceeding 100 to 200 A), a smooth build up of current should be insured at the instant of striking the are from some minimum value until a rated value is obtained corresponding to a current at which the article is processed. A sharp increase of the plasmatron working current from zero to rated is not tolerated, since it leads to an emergency (formation of two arcs, i.e. cathode nozzle and nozzle article), increasing the cathode erosion, thereby reducing its service life term, causing sputtering of metal and deteriorating the quality of the article.

In the known power supply source hereabove described, no means are provided for a smooth current rise at the instant of striking of the plasmatron are.

It is an object of this invention to provide for smooth build up of arc current, during the starting time, from some minimum to a rated value corresponding to a current at which the article is being processed.

The object of this invention is to provide a plasmatron power supply source transformer designed so that during the starting time the plasmatron are current is increased smoothly from some minimum value to a rated value corresponding to a current at which the article is being processed.

This and other objects are attained in a plasmatron are power supply source comprising an inductivecapacitance current stabilizer connected with its output to primary windings of the transformer, the secondary power windings of which are connected through a rectifier to the are gap of cathode article, wherein, according to the invention, the transformer has auxiliary windings coupled magnetically with power windings through its core and connected through an auxiliary rectifier to a capacitor, resulting in that the current flowing through the power windings builds up smoothly as the capacitor charge increases.

An advantage of the plasmatron are power supply source of the invention consists in that it insures a smooth current rise through the power windings and, hence, of the arc current during the start-up period, due to re-distribution of current across the power and auxiliary windings. Duplex arc formation is eliminated, cathode erosion is reduced and the quality of processed article is improved.

It is preferable to connect a resistor parallel to the capacitor with the aim of discharging the latter as the power supply source is disconnected from the power supply.

The invention will now be explained in greater detail with reference to an embodiment thereof is represented in the accompanying drawings, wherein:

FIG. 1 is a block diagram of the power supply source, according to the invention and;

FIG. 2 depicts current curves of capacitor charge, are current and transformer primary winding current at the instant the plasmatron is started.

The plasmatron arc power supply source comprises a three-phase inductive-capacitance stabilizer 1 (FIG. 1), such as a resonant circuit formed by chokes and capacitors connected in a T-network known in technical literature as Boucherot circuit.

The stabilizer 1 input is connected through a group of normally open contacts 2 across the A.C. supply. The stabilizer 1 output is connected across primary windings 3 of the power transformer 4, having secondary power windings 5 and additional auxiliary windings 6. The power windings 5 through a rectifier 7 are connected to the are gap of cathode 8 article 9. The auxiliary windings 6 are fitted on the core of transformer 4, and thus are magnetically coupled with the power windings 5. The windings 6 through an auxiliary rectifier 10 are connected across the capacitor 11. The capacitance of the latter is selected such that at the instant the plasmatron arc is ignited, the current will first flow substantially through the windings 6 and then redistribute across windings 5 as the capacitor ll gets charged.

The capacitor ll capacitance can approximately be determined by the formula where k is the transformation ratio between the windings 5 and 6;

t is the time required for smooth build-up of plasmatron arc (usually 3 to 4 sec);

U is the voltage across the capacitor;

1 is the mean value of the plasmatron arc current.

In parallel to the capacitor ll is connected resistor 12, intended for discharging the capacitor 11 after the power source has been disconnected from the supply. In order to close and open the capacitor-resistor circuit, normally closed contacts 13 are provided. For striking the auxiliary arc of plasmatron cathodo 8 noule 14, there is provided an igniting means 15 such as a low-powered d.c. source and oscillator.

The power source hereinabove described operates as follows:

For striking the plasm atron arc, contacts 2 are made to close and contacts 13 are made to open, and igniting means 15 are switched on simultaneously. The are gap of cathode-nozzle is punctured and an auxiliary are is established between them, owing to which the ionization of the cathode-article arc gap is insured. With the closure of contacts 2, voltage is applied across windings 3 of the transformer 4.

Meanwhile, owing to capacitor 11, the load current of the transformer 4 during the initial period flows through windings 6 and, as the capacitor 11 is charged,

is diminished smoothly as shown in FIG. 2, where i is the current flowing through the windings 6. As the current drops down across the windings 6, the current across the windings 5 increases, as shown in FIG. 2. With the change of currents flowing through the windings 5 and 6, the current i in the primary windings 3 remains stable owing to inductive-capacitance stabilizer l, as shown in FIG. 2, at each instant, equal to the sum of values of currents i and i brought to the primary winding values.

Thus the power supply source hereabove described insures a smooth build-up of plasmatron arc current at the start-up time. The time of smooth build-up of current can be regulated by selecting the characteristics of capacitor 11.

As the contacts 2 are opened for switching off the power source, contacts 13 are closed and the capacitor 12 discharges through the resistor 12, after which the power source is ready for subsequent switching on for performing the above described operations.

In the above, rectifiers 7 and 10 are obviously isolated from each other in a DC. sense, being coupled only through the transformer 4. It is equally clear that capacitor 11 is similarly isolated from rectifier 7.

The usage of the power supply source hereabove described makes it possible to increase the reliability of plasmatron operation and improve the quality of finish of the article.

What is claimed is:

l. A power supply source for supplying a plasmatron arc in a cathode-artiele arc gap with stabilized current, said power supply being operative from a three-phase supply line and comprising an inductive-capacitance stabilizer including output terminals connected to the three phases of said supply line, said stabilizer further including input terminals, a transformer including a primary winding connected to the input terminals of said stabilizer, said transformer also including first and second secondary windings, first and second rectifiers including input terminals connected to respective of the secondary windings of said transformer and further including output terminals, the output terminals of said first rectifier being connected across the cathode-arti cle arc gap for supplying the plasmatron with current, and a capacitor, the output terminals of the second rectifier being connected to said capacitor such that the arc current increases smoothly as the capacitor is charged, said rectifiers being isolated from each other in a DC. sense, said capacitor being isolated from said first rectifier in a DC. sense.

2. A power supply source as claimed in claim 1 comprising a resistor having one terminal connected to the capacitor, and a switch connected between said resistor and said capacitor to discharge the latter after rated are current has been achieved.

3. A power supply source as claimed in claim 2 comprising a further switch connecting said stabilizer and said supply line, said further switch being normally open and the first said switch being normally closed.

4. A power supply source as claimed in claim 2 wherein said capacitor is coupled by said transformer and stabilizer to the three-phrases of the supply line. 

1. A power supply source for supplying a plasmatron arc in a cathode-article arc gap with stabilized current, said power supply being operative from a three-phase supply line and comprising an inductive-capacitance stabilizer including output terminals connected to the three phases of said supply line, said stabilizer further including input terminals, a transformer including a primary winding connected to the input terminals of said stabilizer, said transformer also including first and second secondary windings, first and second rectifiers including input terminals connected to respective of the secondary windings of said transformer and further including output terminals, the output terminals of said first rectifier being connected across the cathode-article arc gap for supplying the plasmatron with current, and a capacitor, the output terminals of the second rectifier being connected to said capacitor such that the arc current increases smoothly as the capacitor is charged, said rectifiers being isolated from each other in a D.C. sense, said capacitor being isolated from said first rectifier in a D.C. sense.
 2. A power supply source as claimed in claim 1 comprising a resistor having one terminal connected to the capacitor, and a switch connected between said resistor and said capacitor to discharge the latter after rated arc current has been achieved.
 3. A power supply source as claimed in claim 2 comprising a further switch connecting said stabilizer and said supply line, said further switch being normally open and the first said switch being normally closed.
 4. A power supply source as claimed in claim 2 wherein said capacitor is coupled by said transformer and stabilizer to the three-phrases of the supply line. 